1. Technical Field
The present invention relates to a virtual image display device which presents a video formed by an image display element or the like to an observer, and particularly, to a virtual image display device suitable for a head-mounted display which is mounted on a head of the observer.
2. Related Art
Various systems have been proposed as an optical system which is incorporated in a virtual image display device such as a head-mounted display (hereinafter, also referred to as HMD) which is mounted on a head of an observer. (for example, JP-A-2002-116799).
As for virtual image display devices such as an HMD, it is desirable to increase an angle of view of video light and to reduce a device weight. Particularly, it is important to reduce a thickness in a visual axis direction of an observer and to move the center of gravity closer to the observer, in order to improve a fit.
When a field of view of an observer is completely covered and only video light is thus viewed, the observer cannot grasp a state of an external world, and thus uneasiness is caused. Furthermore, a new use such as virtual reality is generated by showing an external world and a video in a superimposed manner. Therefore, it is desirable to use displays which display video light in a superimposed manner without disturbing the field of view of the external world.
In virtual image display devices, it is necessary to prevent the generation of ghost light resulting from video light and the like, in order to visually recognize a good image and an external image. Particularly, when a see-through function for displaying external light and video light in a superimposed manner is provided, ghost light may be generated due to not only the video light, but also the external light, and thus a countermeasure for ghosting is more important. Furthermore, it is thought that when trying to secure optical paths of the external light and the video light under the circumstance where the devices have a form similar to glasses and are reduced in size, a position where ghost light is generated is formed even by, for example, a slight optical path deviation which is caused by an error of the product. Furthermore, it is also thought that an observer moves the direction of eyes to see an external world in a see-through mode. In this case, the observer may not see ghost light when seeing an image from the front, but may see the ghost light when moving the direction of eyes.
For example, JP-A-2002-118799 proposes that a frame-like light-shielding member is provided so that flare light and ghost light do not reach eyes of an observer. However, when the light-shielding member is provided as in the case of JP-A-2002-118799, necessary light may be blocked according to alignment upon arrangement, and ghost light may be generated due to components reflected on a side surface of the light-shielding member. Particularly, when a see-through function for displaying external light and video light in a superimposed manner is provided, it is also necessary to consider the occurrence of ghosting by the external light, in order to suppress the generation of the ghost light. Thus, the countermeasure for ghosting using the light-shielding member may be insufficient.